1. Field of Invention
Generally this invention relates to a steering assembly for supporting the wheel of a wheeled vehicle for steering movement relative to the frame of the vehicle, and more particularly to improvements in bicycles, motor bicycles and the like, especially for use in competitive or off-road cycling where an increase in strength and serviceability of said steering assembly is an advantage.
2. Description of Prior Art
A recent increase in interest in off-road vehicle sports has generated a demand for bicycles, motor bicycles, and the like that must withstand increased loads and impact with uncertain ground surfaces.
Heretofore a wide variety of steering assemblies have been proposed and implemented for wheeled vehicles.
Traditional steering assemblies are brazed or welded together from separate parts into a final assembly. The parts typically joined together by this process are the blades, steerer, crown, and reinforcements. The fork assembly in U.S. Pat. No. 609,937 to Kelly 1898, Aug. 30, had a frame stem, curved fork blades, and crown brazed together.
The front fork crown assembly in U.S. Pat. No. 641,858 to Halifax, 1900, Jan. 23 had a V-shaped assembly without separate fork blades that was brazed or welded into final assembly. The front steering fork in U.S. Pat. No. 576,831 to Accles and Renout, 1897, Feb. 9 had the crown mechanically attached to the steering stem with the crown integral with the fork blades. The steering fork in U.S. Pat. No. 623,507 to Barnish 1899, Apr. 25 provided splineways to receive splines on the end of the fork arm.
The welding or brazing process used in these designs reduces the strength of the material in the vicinity of the weld. The affected area of the steering assembly is called the heat affected zone. The losses in strength are due to the heat treating effect of the joining operation, either tempering, or annealing and tempering the assembly material. Typical losses for high quality steel forks are on the order of thirty percent in yield strength.
Users of wheeled vehicles, especially off-road and competitive bicycles and motor bicycles regard this type of assembly as unsatisfactory because of the high failure rate of this type of steering assembly when subjected to significant impact and bending loads.
Steering assemblies are structures that are subject to cantilever bending forces that act on the blades. Cantilever forces are those in which the beam that supports the load is not reinforced by any structure other than that at the attached end or by reinforcing the beam itself.
The design of current steering assemblies causes the highest bending loads to be concentrated at the heat affected zones. This makes the overall strength of the blades low compared to the potential strength of the material used. The traditional method of constructing steering assemblies for bicycles, motor bicycles and the like, makes this undesirable situation inevitable.
Off-road bicycles and other wheeled vehicles ridden for sport and recreation are a recent development. These wheeled vehicles, unlike vehicles designed for use on paved surfaces, are frequently subject to very high stress loads. The combination of uncertain ground surfaces and landing on the ground after jumping high in the air leads to significant impact and bending loads on the steering assembly. Traction in some circumstances may be very high and the load on the steering assembly under braking significant.
The steering assemblies and frames for these vehicles have evolved from traditional designs and methods. The current off-road steering assembly regularly fail as a result of the loads described. This is a result directly related to the design and construction of these assemblies and demonstrates the need for a new approach to this problem. This is especially true for sporting and competitive applications.
A further problem with current designs is that when damaged the user's alternatives are to replace the entire blade assembly or have the blade repaired by a specialist. The typical user cannot repair the steering assembly with simple hand tools. The cost of having the specialist repair the blade is frequently higher than the cost of the new blade.
The demands on the steering and handling characteristics of off-road wheeled vehicles vary with the riding conditions. The steering assembly is an integral part of the vehicle whether bicycle, motor bicycle or the like. Traditional steering assemblies offer no adjustment possibilities other than replacement with new blades of different dimensions.
Most users, therefore, would find it desirable to have a steering assembly that could Withstand the loads and stresses of off-road travel, be adjustable and serviceable should any component of the assembly fail, and have the option of replacing individual components rather than the entire assembly.